davepb port has covered energy and the environment for congressional quarterly. i want to go to richard on the independent line. caller: good morning. thanks for taking my call. i'm curious as to why we are always advised that global warming is such a terrible thing when in reality we know over history is world has gone through temperature changes and climate changes to such a degree that they were massive. for instance, between the years 800 and 1300 the world had warmed up such that greenland had 10 to 15,000 people. the catholic church had a pope there and they raised hay and cattle and this went on for years. why sit so terrible we have to consider it a bad thing? it's a political issue and that's all it is. guest: scientists will tell you the globe has gone through cycles of warming and cooling throughout the existence of humans. they will also tell you right now the global atmosphere is warmer than it's been in the last 650,000 years. and that we've seen a spike in warming that corlates directly with a spike of fossil fuel emissions that have been produced